The following abbreviations are herewith defined, at least some of which are referred to within the following description.
3GPP Third Generation Partnership Project
CCA Clear Channel Assessment
CSS Common Search Space
DL Downlink
ECCA Extended Clear Channel Assessment
eNB Evolved Node B
ETSI European Telecommunications Standards Institute
FBE Frame Based Equipment
FDMA Frequency Division Multiple Access
LAA Licensed Assisted Access
LBE Load Based Equipment
LBT Listen Before Talk
LTE Long Term Evolution
MCS Modulation and Coding Scheme
MU-MIMO Multi-User, Multiple-Input, Multiple-Output
OFDM Orthogonal Frequency Division Multiplexing
PCell Primary Cell
PUSCH Physical Uplink Shared Channel
QoS Quality of Service
RRC Radio Resource Control
SC-FDMA Single Carrier Frequency Division Multiple Access
SCell Secondary Cell
TBS Transport Block Size
TDD Time-Division Duplex
TDM Time Division Multiplex
UE User Entity/Equipment (Mobile Terminal)
UL Uplink
UMTS Universal Mobile Telecommunications System
WiMAX Worldwide Interoperability for Microwave Access
In Wireless Communications networks, for example, in LTE systems using LAA, an unlicensed spectrum is used with assistance from a licensed carrier. LAA may facilitate a fair coexistence with other technologies over the unlicensed spectrum and satisfy various regulatory requirements in different countries and regions.
For regulation requirements in Europe, ETSI has specified two channel access mechanism (i.e., FBE and LBE). For these two channel access mechanisms, before starting transmissions on an operating channel, the equipment (i.e., FBE and LBE) may perform a CCA check by using energy detection with the CCA observation time not less than 20 microseconds (“us”). If the energy level in the channel does not exceed a predefined threshold corresponding to the power level, the equipment may consider the operating channel to be clear and may transmit immediately. In contrast, the equipment may consider the operating channel to be occupied and may continue to perform the CCA check. For FBE, the equipment may continue to perform the CCA check at an end of a frame period. For LBE, the equipment may start performing ECCA immediately until it can grab the channel. In some situations, LBE may have a higher channel access probability than FBE.
Although LBE may have a higher channel access probability than FBE, FBE may be more appropriate for LAA UL. For example, FBE can follow the LTE UL framework that a UE's UL transmission should be permitted by a serving eNB, FBE can avoid inter-UE blocking and enable UL multiplexing of multiple UEs in one subframe by FDMA and MU-MIMO, FBE does not require a reservation signal, and FBE has a fixed timing relationship and UL transmission can always start from the first OFDM symbol of a subframe. Accordingly, in certain configurations, FBE may be used as a baseline for LAA UL operation. In contrast, LBE may be more appropriate for LAA DL.
FBE may have certain drawbacks. For example, in certain implementations, the frame period in FBE is related to the performance of LAA UL. In such configurations, fixed LAA DL/UL scheduling may decrease throughput. Furthermore, in one configuration, long frame periods may limit opportunities to use the unlicensed band. In addition, FBE may have a large overhead due to the reservation of the idle period at the end of each frame period.
Seven TDD uplink/downlink configurations with 5 millisecond (“ms”) or 10 ms DL-to-UL switching-point periodicity have been defined for TDD systems. However, because of regulatory requirements due to LBT rules and the traffic adaptation in UL and DL, the seven existing TDD uplink/downlink configurations may not facilitate efficient DL and UL resource usage in LAA.